This invention relates to a hydraulic control device for use in an automatic transmission. More particularly, this invention relates to a hydraulic control device for use in an automatic transmission which reduces shock during a gear shift into a forward drive condition such as drive (D), second (2nd), or low (L).
As well known in the art, automatic transmissions include types having a torque converter and a planetary gear unit with a clutch located therebetween. The clutch is similar to a clutch element of a manual transmission which lies between an engine and a gear train. When the gear transmission is shifted to a D, 2nd, or L position, the clutch is hydraulically actuated so as to be brought into engagement. Consequently, power is transmitted from the torque converter through the planetary gear unit by engagement of the clutch to an output shaft, and a forward drive condition is established. During this operation, a working fluid pressure is directly supplied to a piston chamber of the clutch without being hydraulically controlled, and the clutch is engaged in a quick and sudden response. This sudden power transmission causes an unsatisfactory heavy shock.
Accordingly, it is a primary object of this invention to provide a new and improved hydraulic control device which can be used in automatic transmissions to eliminate the above-described problems.
Another object of this invention is to provide a new and improved hydraulic control device for use in automatic transmissions of the type having a frictional engagement device between a torque converter and a planetary gear unit to smoothly bring the device into engagement when actuated.
Still another object of this invention is to provide a new and improved hydraulic control device for use in an automatic transmission that smoothly brings a frictional engagement device into engagement when actuated by modulating the fluid pressure supplied to it.
It is a further object of this invention to provide a new and improved hydraulic control device for modulating fluid pressure to a frictional engagement device that is reliable and conserves on space.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the hydraulic control device of this invention is for automatic transmissions of the type having an input shaft, an intermediate shaft coupled to the input shaft through a hydraulically actuated frictional engagement device during a forward drive condition, servo means for hydraulically actuating the frictional engagement device, an output shaft operatively connected to the intermediate shaft through a planetary gear mechanism, a hydraulic fluid pressure source, a manual shift position selector mechanism for establishing a forward drive condition, and channel means for supplying fluid pressure from the fluid pressure source to the servo means when a forward driven condition is established by the shift position selector mechanism, and comprises means for modulating the increased fluid pressure supplied by the channel means to the servo means upon actuation of the frictional engagement device for minimizing shock as the intermediate shaft is coupled to the input shaft during shift into a forward drive condition.
Preferably, the modulating means includes accumulator means connected with the channel means for moderating the increased fluid pressure supplied to the servo means by the channel means when the frictional engagement device is to be actuated, and wherein a fixed member is located adjacent to the output shaft for mounting the accumulator means.
It is also preferred that the modulating means further includes an orifice and a check valve disposed in parallel to each other in the channel means, the check valve being closed and the orifice reducing the increased fluid pressure supplied to the servo means by the channel means when the frictional engagement device is to be actuated.
The invention consists in the novel parts, constructions, arrangements, combinations and improvements shown and described. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one embodiment of the invention and, together with the description, serve to explain the principles of the invention.